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题名: 壳斗科(Fagaceae)的系统演化及生物地理
作者: 陈亚琼
学位类别: 博士
答辩日期: 2007-01-11
授予单位: 中国科学院昆明植物研究所
授予地点: 昆明植物研究所
导师: 周浙昆
关键词: 壳斗科 ; 系统演化 ; RPB2 基因 ; 形态演化 ; 生物地理 ; 化石
学位专业: 植物学
中文摘要: 本文首次利用核基因RPB2(编码RNA聚合酶II的第二个大亚基)序列构建了壳斗科Fagaceae 的系统关系,并对RPB2基因的分子进化、壳斗等重要形态性状的演化及生物地理开展了相关的研究,主要结果如下: 1. 分子系统学 基于RPB2编码序列的系统关系表明壳斗科是一个单系类群,榛木科Corylaceae是壳斗科的姐妹群,南水青冈科Nothofagaceae不是它的姐妹群和成员。在壳斗科内部,水青冈属Fagus是基部类群,三棱栎属Trigonobalanus是次基部类群,三棱栎的姐妹群是一个包括了金鳞果属Chrysolepis、石栎属Lithocarpus、栗属Castanea、栲属Castanopsis和栎属Quercus的分枝,其中具有壳斗内裂瓣的金鳞果属可能与其他具种子地下萌发特征的4个属有较近的共同祖先,但是该关系有待进一步验证。基于RPB2基因的壳斗科分子系统关系与形态性状和其他多个分子系统结果相吻合,是一个新的适合于壳斗科系统研究的分子工具。 2. RPB2基因的分子进化 本文研究了RPB2基因10个外显子区域(第2到第10)。该区域碱基序列GC含量的变化与序列(包括附近的内含子)的变异程度呈正相关。其中外显子3、5、6、7、8区域中碱基替代频繁(R>1),是RPB2基因变化较快的区域。发现本区段有28个氨基酸替代位点,其中有14个仅发生在壳斗目内部,主要分布于外显子2、3、4、5和8,这些氨基酸突变位点被定位到RNA聚合酶的第二个大亚基的蛋白质晶体三维结构上,其中9个位点位于非二级结构域,另5个位点分别位于α-螺旋和β-折叠上。而外显子3编码的氨基酸序列中存在最多的替代位点最多。部分氨基酸替代位点很接近POLII的活性中心。这些变异位点与壳斗目和壳斗科的系统位置有联系。这些结果为从蛋白质大分子三维结构上揭示壳斗目中类群演化关系提供了重要线索。 3. 壳斗的起源与演化 壳斗科的壳斗系单源起源,来源于二歧聚伞花序(dichsia )最外侧小枝,与其他类壳斗结构(cupule-like structure)不同。依据RPB2基因序列重建的系统关系支持壳斗多向演化的假说(F+1的规律,壳斗裂瓣数目比二歧聚伞花序中小花数目多1)。在各种壳斗类型中,具2果4裂瓣的水青冈类型保持了原始的性状,三棱栎型壳斗是较晚分化的类型,具有壳斗内裂瓣的金鳞果类型壳斗与其他类型壳斗有较近的共同祖先。 RPB2系统与其他3种分子系统共同支持了壳斗演化的规律:壳斗裂瓣从开裂到融合、壳斗形态从复杂到简单、壳斗横切面形状从三角型到圆型。从晚白垩世桑托尼阶(Santonian )到渐新世(Oligocene),不同类型壳斗化石出现的时间顺序和多个壳斗科分子系统关系的一致性与推断的壳斗演化过程相吻合。来自现代分子生物学和化石证据相互引证,支持壳斗多向演化的假说。壳斗演化规律的重建有利于进一步探索壳斗科的系统关系和演化历史。 4. 形态性状的演化 基于表皮毛形态性状的分支分析及在RPB2分子系统关系重建演化历史,发现表皮毛性状有4种演化类型:同塑类型、一次性起源、属特有类型、多次起源和丢失类型。随着壳斗科类群的发展,表皮毛向着具有类型多样化、结构复杂化的方向演化。 RPB2系统关系表明壳斗科内可能有2次风媒起源。演化早期有一次风媒起源(形成水青冈属),后期发生第二次风媒起源(形成栎属),原始的虫媒性状通过三棱栎(T.verticillata)-> 石栎属、栗属和栲属的传代线得以保持。 5. 壳斗科的新系统 根据多种分子系统关系,结合形态性状分析,提出了壳斗科的新系统包括3个亚科:水青冈亚科Subfamily Fagoideae Oersted、三棱栎亚科Subfamily Trigonobalanoideae Lozano-C和栗亚科Subfamily Castaneoideae Oersted,2个族和7个属。 水青冈亚科包括水青冈属;三棱栎亚科包括广义三棱栎属;栗亚科包括金鳞果属、石栎属、栲属、栗属及栎属。按照传粉方式的不同,栗亚科分为2个族,虫媒的栗族Tribe Castaneae Schwarz和风媒的栎族Tribe Quercueae Schwarz,栗族包括金鳞果属、石栎属、栲属和栗属;栎族包括栎属。水青冈亚科和三棱栎亚科保留了较多原始性状,并处于多个分子系统中较基部的位置,属于低等壳斗类(the “lower” Fagaceae);栗亚科具有更多的衍生性状,属于高等壳斗类(the “higher” Fagaceae)。 6. 生物地理学 壳斗科的祖先分布区是一个广阔的区域,包括了欧亚-北美大陆的温带、热带和亚热带的现代分布区及化石种分布区。随着大陆漂移的运动,连续的祖先分布区被隔离,全球气候变化和不同类群的适应性差异使各分布区内的类群发生隔离、灭绝或扩散。三棱栎洲际间断分布格局的形成代表了壳斗科现代分布形成的部分实事。 亚州东南部可能是壳斗科的次生演化中心,低等壳斗类在该区域的再次发展对形成高等壳斗类及其现代分布有重要影响 。低等壳斗类的现代分布区是北半球广布的祖先分布区收缩后的孑遗区(也有一定的扩张),而高等壳斗类的泛北极现代分布区可能是在亚洲东南部次生演化后再次扩散的结果。在地理分布特征上,祖先分布区广布是低等壳斗类的分布特征,而高等壳斗类则具有现代分布相对连续和广布的特征。
英文摘要: The RPB2 gene (codon the second largest subunit of RNA polymerase II) was used to reconstruct the phylogeny of the Fagaceae. The evolution of some morphological characters, and their biogeography patterns, are discussed, and a new taxonomic system of the Fagaceae is proposed. The main conclusions are summarized follows 1. RPB2 molecular phylogeny A fragment of the RPB2 gene, a type of low copy nuclear gene that encodes the second largest subunit of RNA polymerase II, was used to investigate the phylogeny of the Fagaceae. The phylogeny of the RPB2 gene, based on sequences from exon 2 to exon11, indicated that the family Fagaceae was a monophyletic group and the family Nothofagaceae was not a sister group of it. In the Fagaceae, the genus Fagus is in the basal position, followed by the genus Trigonobalanus, a sister clad that includes the genera Chrysolepis, Castaneae, Castanopsis ,Lithocarpus and Quercus. The phylogeny of RPB2 suggested the genus Chrysolepis and shared a closer common ancestor with the the clade cortained genus Castaneae, and the genus Castanopsis and the genus Lithocarpus, but more evidence is needed to confirm this relationship. The RPB2 phylogeny was compatible with morphological characters evolution and with other molecular phylogenic hypotheses; therefore, it is a potentially valuable nuclear tool for phylogeny work in Fagaceae in the further. 2. The molecular evolution of RPB2 gene in Fagales Ten exons (2nd to 11th) of the RPB2 gene (1271bp) were investigated. The degree of GC content variation was positively related with sequences changing in this region including introns. The base substitutions in exons 3, 5, 6, 7, 8 were higher than those in other exon regions. Changes in amino acids frequencies in RPB2 were coincident in 18 species. Compared with the outgroup, there were 28 amino acid substitutions, 14 of which occurred in the Fagales, distributed in exons 2, 3, 4, 5 and 8. This indicates that the RPB2 gene might be impacted by positive selection. Fourteen amino acid substitutions were located at the three-dimensional protein structure of intact RPB2 gene’ s product, 9 sites of which were located in the lower complex linker regions and 5 sites at the alpha- hylex and belta- sheet. These results provide important insights to the evolution of the Fagales using the three-dimensional structure of proteins. 3. Origion and evolution of cupule The cupule is the most distinguishable character of the Fagaceae and has been the focus of much research. Many hypotheses have been proposed for the origin, evolution and morphological features of the cupule. These have been based on different types of evidence, but here we will use molecular phylogeny and fossil evidence. Our results support the view that cupule valves originated from the outest branches of dichasium, and that cupules of the Fagaceae are diagnostic from other cupule-like organs with perianth origination in Fagales. There are three models of cupule evolution each characterized by distinct evolutionary tendencies, single, two and multi-directional respectively. Based on these models, we reconstructed the cupule’s evolution using the consensus of four recent molecular phylograms from different DNA fragments. Our results indicate that cupules were monophyletic and that the Fagus cupule, with four cupule valves enclosing two triangular acorns, was the ancestral type, Trigonobalanopsis cupule was the inferior-ancestral type, and the Chrysolepis cupule which possesses inner valves, shared a common ancestor with other roundish cupules. Our conclusions are also unequivocal supported by fossil evidence, with affinity of extant homologous cupule. The consensus from the different molecular phylogeny hypotheses along with the age of fossil cupules that are similar to extant Fagaceae taxa, indicate that the cupule evolved in multi-directions, and that the small triangular narrow winged fruits surrounded by a dehiscent cupule was plesiomorphic, and that a bigger roundish fruit surrounded by an indehiscent cupule was synapomorphic. All those results provide the new evidence to explore evolution and phylogeny of Fagaceae. 4. Character evolution The twenty-one trichomes characters were cladistic analysised and were mapped on the RPB2 phylogram. The results demonstrated 4 types of trichome evolution: the plesiomorphy, the synapomorphy, the diagnostic of genus, and the apomorphy with several origins. The trichome characters are more complex and diverse in derived lineages of the Fagaceae. Oldest Fagaceae fossil (late Cretaceous, Santonian) supported anthophilous pollination was ancestral model, based on this, RPB2 molecular phylogeny interpreted that 2 origins of anemophilous pollination occurred in Fagaceae independently. Therefore, 2 kinds of pollination syndrome evolved in Fagaceae parallelly. Additionally, the evolution of other characters related with pollination strategy, such as flower structure, sex and axis of inflorescence and morphology of pollen grain probably be constrained by pollination syndrome. 5. New system of Fagaceae Based on the molecular phylogenies and morphological analysis, a new taxonomic system of the family Fagaceae is proposed, that includes 3 subfamilies (Subfamily Fagoideae Oersted, Subfamily Trigonobalanoideae Lozano-C, and Subfamily Castaneoideae Oersted) and 2 tribes (Tribes Castaneae Schwarz, Tribes Quercueae Schwarz).The Subfamily Fagoideae includes the genus Fagus, and the Subfamily Trigonobalanoideae includes the genusTrigonobalanus s.l.. According to the pollination strategies, the Subfamily Castanoideae was divided into 2 tribes (tribes Castaneae Schwarz and Quercueae Schwarz). The Anthophilous tribe Castaneae includs the genus Chrysolepis, Lithocarpus, Castanea, and Castanopsis, and the anemophilous tribe Quercueae is composed of the genus Quercus. Some diagnostic primary characters shared by the Subfamilies Fagoideae and Trigonobalanoide indicate that these 2 subfamilies are the “lower” Fagaceae. With more derived morphyology characters, Subfamily Castaneoideae is the “higher” Fagaceae. This new system is supported independently by the fossil records and the consensus of several molecular phylogenies from different DNA fragmants. 6. Biogeography study The wide fossil distribution indicates that the ancestral area of the Fagaceae was a continuous Holactica area including temperate, subtropical and tropical Northern Hemisphere, formed at least before the Santonian during the Cretaceous though NALB, BLB or Malpighiaceae route. Before the early Paleocene, these continuous ancestral areas were separated by continental drift. Simultaneously, climate deterioratied from later Paleocene and the diversity of adaptations in the different groups have controlled the vicariance, dispersal and extinction of Fagaceae groups in all subareas. A secondary origin center of the Fagaceae is proposed for Southeast Asia, for rich diversity of genus and species for 3 subfamilies, especially in advanced subfamily Castaneoideae. Possibly, the “higher” Fagaceae originated directly from the “lower” Fagaceae in Southeast Asia. The current disjunctive and narrow distributions of the“lower” Fagaceae were relics of wider ancestral distribution. However, the continuous and wider current distribution of the “higher” Fagaceae was the outcome of re-dispersal from secondary origination in Southeast Asia.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.kib.ac.cn/handle/151853/68
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壳斗科(Fagaceae)的系统演化及生物地理.陈亚琼[d].中国科学院昆明植物研究所,2007.20-25
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